The present invention generally relates to electrical insulators for magnetic cores, and more particularly, to a system and a method for placing slot cell insulators into stator cores of dynamoelectric machines.
Dynamoelectric machines, such as electric motors and generators, include stator cores which generally are formed of a plurality of steel laminations bonded together to form a hollow cylinder having a pair of end faces spaced apart a longitudinal distance referred to as the stack height. A plurality of teeth extend from an inner cylindrical surface of the core into a hollow center portion. The teeth form slots between adjacent teeth that extend the length or the height of the core.
Electrical conductors are disposed in the slots to react to or to generate electromagnetic fields. Generally, the conductors are coils of wire wrapped around the teeth and through the slots in a winding pattern. In an electric motor, for example, energizing the coils generates an electromagnetic field in the core to rotate a rotatable assembly in the center portion of the core. To generate the electromagnetic field and to prevent shorting, the core is electrically insulated from the coils of wire. One desirable approach is the employment of slot cell insulators fabricated from suitable insulating or dielectric material.
One type of slot cell insulator is formed by folding opposite ends of a piece of relatively thin dielectric material upon itself along parallel fold lines extending across a width of the material to form two end portions of at least double thickness dielectric material. This piece of material is then folded lengthwise along a longitudinal fold line extending approximately through the center of the material with the folded end portions on the outside. In use, a center portion of the insulator lines the walls of the slots in the stator core and prevents contact between the conductors and the stator core. The folded-over end portions form cuffs which engage respective opposite end faces of the stator core when the insulator is placed in the slot. The cuffs help the insulators remain within the slots in the stator core.
One method of inserting slot cell insulators into a stator core includes a device having a crank and slider mechanism for driving a push rod. The push rod engages a cuffed end of an insulator and longitudinally pushes the insulator past an end face and into a slot in the stator core. This method requires incrementally, rotatably indexing the stator core to position each slot to receive an insulator. Indexing the stator core to the precise position accurately and consistently is difficult, however. If the stator core is not positioned precisely, the insulator may catch on the end face adjacent the slot as the insulator is inserted.
Not only is this a slow process, but the device is difficult to adjust for different lengths of insulators used in stator cores having a different stack height. Often an entirely new device must be substituted. Furthermore, in this type of device the insulators cannot be formed until a stator core can receive them, thus the device is idle between stator cores.
In addition, the slider-crank mechanism requires an extensive amount of maintenance to ensure precise positioning of the insulator in the slot. Inserting one insulator at a time also means that incrementally rotating the stator core through three hundred and sixty degrees holds the stator core at a slot cell insulator inserting station on an assembly line for a long time.
Another problem with the prior insulator insertion devices is that sometimes on one side of the longitudinal fold in the insulator there is more material than on the other side of the longitudinal fold and thus the longitudinal side edges do not line up evenly. As a result, when the insulator is placed into a slot in the stator core, a portion of the tooth or other part of the stator core is exposed and the chances for a short circuit increase.
The present invention concerns a system and a method for loading slot cell insulators into a stator core of a dynamoelectric machine. According to one aspect of the invention, the system includes a forming assembly, a transfer mechanism and a loading assembly. The forming assembly forms the slot cell insulators from electrically insulating sheet material. The transfer mechanism transfers the insulators from the forming assembly to the loading assembly. In moving the insulators from the transfer mechanism to the loading assembly, the longitudinal side edges of the insulator automatically even up, for example, as is explained below. When the loading assembly is full and the stator core is in position, the loading assembly simultaneously loads the insulators into slots extending the length of the stator core. The system forms slot cell insulators substantially continuously and stores them in the loading assembly. When the stator core is ready to receive the insulators, the loading assembly simultaneously loads the insulators into the slots in the stator core. Thus, the system and method according to the present invention load slot cell insulators into the slots of a stator core with improved efficiency.
According to one aspect of the invention, the system includes a forming assembly which forms a slot cell insulator having a generally U-shape cross-section. The system also includes a loading assembly which stores the slot cell insulator. A transfer mechanism is interposed between the forming assembly and the loading assembly to transfer the slot cell insulator from the forming assembly to the loading assembly. The loading assembly is adapted to store and subsequently to load simultaneously a plurality of slot cell insulators into the slots in the stator core.
According to another aspect of the invention, the method includes forming a slot cell insulator having a generally U-shape cross-section; turning the slot cell insulator so that an open end of the generally U-shape slot cell insulator faces a loading assembly; moving the turned slot cell insulator into the loading assembly; repeatedly forming, turning and moving slot cell insulators until a plurality of slot cell insulators are stored in the loading assembly; and pushing the plurality of slot cell insulators simultaneously from the loading assembly into the slots of the stator core.
According to another aspect of the invention, the system includes a means for forming a slot cell insulator having a generally U-shape cross-section; a means for storing the slot cell insulator; a means for transferring the slot cell insulator from the forming means to the storing means; and a means for simultaneously loading a plurality of slot cell insulators from the storing means into the slots in the stator core.
According to yet another aspect of the invention, the system includes a forming assembly which forms a slot cell insulator having a generally U-shape cross-section; a loading assembly which stores the slot cell insulator in a cartridge; and a transfer mechanism interposed between the forming assembly and the loading assembly to rotate the slot cell insulator one hundred and eighty degrees. The transfer mechanism includes a shuttle plate which cooperates with the forming assembly to transfer the slot cell insulator from the forming assembly to the loading assembly. Furthermore, the loading assembly is adapted to store and subsequently to load simultaneously a plurality of slot cell insulators into the slots in the stator core.
These and other features of the invention are fully described and particularly pointed out in the claims. The following description and annexed drawings set forth in detail one illustrative embodiment of the invention, this embodiment being indicative of but one of the various ways in which the principles of the invention may be employed.